I am doing a reno and the damn things take forever to charge and don’t last long (i got 2 4ft cuts and a two dozen screws installed from two batteries, one used twice, one used maybe a dozen charges in 2 years, both are now on the charger after being fully charged yesterday), can i solder in some 2500mAH NiMH, would they charge ok with the stock charger and could they deliver the Amps a cordless drill or circular saw would draw?
They’ll do better than the pitiful, destroyed cells that are in there now. Good Sub-C cells are probably higher drain than good LSD AA cells such as Eneloop. I doubt that those Sub-C cells were good to start out with.
FWIW I use corded tools for that kind of work.
…batteries always fail after 3-4 years but convenient, no?
ripped from NiMH Battery FAQ
Which are better, NiCd batteries or NiMH batteries?
For most electronic devices it is better to use NiMH batteries than NiCd batteries. NiCd batteries use Cadmium, a highly toxic heavy metal, that can damage the environment if not disposed of properly. (They should be recycled not discarded). NiMH batteries usually have a higher capacity than NiCd batteries of the same size. Some people argue that NiCd batteries deliver faster discharge rates than NiMH batteries. While this may be true under certain circumstances, the difference is not relevant when considering power sources for electronic devices like digital cameras or portable music players. (If you are choosing a battery to drive a high torque power screwdriver, then NiCds can outperform NiMH). NiMH batteries require more sophisticated chargers than those typically used for NiCd batteries. But smart chargers designed especially for NiMH batteries are now readily available.
Bort;
As I understand it there is a danger of a NiCad charger for a tool battery not sensing when the NiMH batteries are fully charged as the electrical signal from the NiMH cells is more subtle than from the original NiCad cells. Battery Junction still carries NiCad batteries in a number of sizes if you want to rebuild the packs to original specifications. Alternatively many battery tools makers now offer Lithium cell battery packs and chargers for them as upgrades for their tools.
Several replies
I don’t have the corded versions, i got them for $20 for drill, circular saw and light, manufactured wk 38-2012, black and decker
It charges at probably 0.1C and does not terminate as it is, its a dumb charger with no termination and no timer. NIMH has a weaker termination signal then NiCad, othereise they are related technologies but in this case it does not matter anyways
I don’t want lithium because they will die in a few years (capacity will be reduced to minimal) and i don’t do enough jobs to justify the higher cost.
The idea to replace them with better sub c cells is a good one, i’ll keep it in mind, it would be a straight plug and play replacement
Trickle charging doesn’t need to be terminated. Bort mentioned that his chargers take “forever,” so may be safe to assume that it’s a trickle charge.
85mW
I think rebuilding the two packs with better cells would cost $15-30 USD each, in cells alone… plus $10 in shipping at BG, so $40-70 together, right? Much more powerful low-end corded replacements should cost you $20 and $30 for the drill and saw respectively… so $50 total.
Inexpensive corded tools are typically anemic. IMO underpowered tools encourage people to do bad/dumb things… hence they are safety issue in addition to an annoyance. I can’t afford or justify the nice big cordless tools either, so I use mid-range corded tools.
EDIT: right, 85mA (or mW?) would certainly be a trickle charge. No problem there. Eneloops cost as much as Sub-C though, so you’ve got the same cost to benefit issue there. Any pack rebuild would cost more than the price of a significantly better corded tool. Unless you have a specific need for cordless stuff of course… building a hidden wilderness bunker maybe?
If you spend some time, and rough up the battery pack, you can recover some, if not all of the capacity, I have found.
I have taken many a 9.6v pack, done a discharge test, and it discharges at ~1a for 30 or so seconds. after I hook it up to a 9v power source, I charge it for a while, the voltage floats up to about 9.2v, and then I use a car headlight to discharge it. Run time will increase dramatically, from under a minute in the beginning, to around 10+ minutes. The discharge capabilities also increase dramatically.
It will not make the pack brand new, but it usually makes them usable again.
not cheap either, i noticed that the circular saw stops working at 50% charge, so at least that cuts the recharge time, but i guess i won’t be bothering to upgrade the batteries, after two more jobs it would be years before i am likely to need much use of these tools.
On the plus side i borrowed a jig saw for some circular cutting
i’ll just have to grin and bear it
Would it be possible to run them directly on a high current 12v PSU? Assuming you have one?
They are 18V, i was actually thinking i could start a business making plug in adapters for people in my situation or who only want to buy one of each tool and go for the cordless version.
Right, an 18v battery made up of Sub-C cells will sag a long way under load. I figure it’ll sag pretty badly - 12v would be 0.8v per cell, it may go even lower than that! A strong 12v PSU will not sag very much, or maybe not at all.
Lots of threads here and/or CPF suggest that NiCADs can often be recovered if you can completely discharge them (even to 0V) and apply a number of suitable charge cycles.
As long as there is no evidence of outgassing or leakage, NiCADs are more likely to be recoverable than old NiMH cells.
The key is to do them individually rather than as a pack.
Fast charge (1C) to avoid crystal formation and slow discharge to dissolve it is apparently the recommended practice with a forming charge or two mixed in.
It may take some time and mucking about but if you are planning to rebuild the pack anyway it might be worth the effort. It won't cost you anything but a bit if time.
I don’t think it will be enough, fully charged its 21V, i assume under load i would get 15ish volts and the circular saw dies at 17.4V (no load) so i am thinking i would need more then the 12V supply could put out.
Those laptop power supplies are something like 19V are they not?
I’m not so sure about that (or I wouldn’t have suggested it ;-)). High current 12v supplies abound (PC PSU, server PSU, hobby PSU, radio PSU), so if you have one it’s easy to check.
Laptop PSUs are quite low current. Good ones may go into protect mode, I dunno what happens to the knockoff/aftermarket ones when you try and pull 10-20A or something from a 3A supply.
i have no spare 12V supply but if i did i would still be hesitant to try it
Why?
high current, no soldering iron, if items damaged i can’t afford to replace them, fear
i have been curious about the same thing as i have a few drills and tools that have dead NiCad packs, but never tried NiMh as the chargers are designed for NiCads only.